Recently, as next-generation nonvolatile semiconductor memories, resistance change memories have been attracting attention, such as a resistive RAM (ReRAM) in which a variable resistive element serves as a memory element, and a phase change RAM (PCRAM) in which a phase change element serves as a memory element.
These resistance change memories are characterized in that a memory cell array is a cross-point type and a higher memory capacity is thus enabled by three-dimensional integration, and also characterized by being capable of the same high-speed operation as that of a DRAM.
In the resistance change memory, the cross-point type memory cell array comprises a plurality of cell units. The cell unit includes a memory element and a non-ohmic element (e.g., see Jpn. Pat. Appln. KOKAI Publication No. 2009-123725).
In connection with the resistance change memory, miniaturization of the cell unit is underway in order to increase the memory capacity.
Along with the advancing miniaturization of the cell unit, problems that have not been arisen in conventional device sizes are being posed.
One of the problems is associated with the material that forms the non-ohmic element.
A device made of silicon such as a PN diode may be used for the non-ohmic element.
When polysilicon is used as silicon for forming the element, morphological roughness (surface roughness) may be caused in the surface of deposited polysilicon. The morphological roughness degrades the state of the junction (interface) between polysilicon and other parts, and leads to characteristic deterioration of the element that uses silicon along with the miniaturization of the element.